Professor Yoram Rubin is also the president of the International Commission on Ground Water, part of the International Association of Hydrological Sciences.

Between
the rows of ripening grapes at the Robert Mondavi Vineyard in Napa
Valley, a UC Berkeley researcher pushes a wheelbarrow outfitted
with a ground-penetrating radar device. The field trip is part
of a project that combines time-tested agricultural methods with
high-technology geophysics to improve the quality of Northern California's
finest wines.

Yoram Rubin, UC Berkeley professor of Civil and Environmental Engineering,
is leading research to map the soil's water content at California
vineyards using data generated from high-frequency radar systems.
The aim is to give grape growers a tool for managing "stressed
irrigation," a technique that keeps the plants a little bit
thirsty, resulting in smaller grapes with better flavor rather
than larger fruit and leafy vines.

"Our approach is noninvasive. There's no drilling, and
we can provide quick and accurate estimates of soil moisture content
over large areas," says Rubin, whose principal collaborator
on the project is his former student Susan Hubbard, now a staff
scientist in Lawrence Berkeley National Laboratory's Earth
Science Division. The project is part of the Institute for Environmental
Science and Engineering (IESE) and the Center for Information Technology
Research in the Interest of Society (CITRIS).

Currently under way at Mondavi and Dehlinger Vineyards, Rubin's
field research originated from an earlier study to monitor and
understand the transport of bacteria through subsurface soil. Rubin
realized that applying a similar noninvasive technique to measure
distribution of water in soil could help conserve water resources
in agriculture. The trick, however, was finding a receptive audience.
Grape growers, he quickly realized, had a lot to gain from knowing
what lies beneath the surface of their vineyards.

To map the subsurface of a vineyard, Hubbard, Rubin, and his graduate
students push a vacuum cleaner-sized radar instrument between
the vines. The device sends high-frequency electromagnetic waves
into the ground to depths of several meters depending on the type
of soil being tested. The velocity of the waves' reflection
is dependent on the ground's dielectric constant, the ability
of a material to store electrical energy under the influence of
an electric field. Soil has a low dielectric constant that is dramatically
elevated in the presence of water. The signal's travel time
is then interpreted as a measurement of soil moisture, much like
data from a medical computed tomography (CT) scan provides physicians
with information about a patient's tissue properties.

Every vineyard's soil will have different characteristics.
At the Dehlinger vineyards, the waves bounce off a natural reflector
in the ground-soil layer with significant variation in
its electrical properties-and return to the radar's
receiver. At Mondavi, there is no natural reflector. Instead, the
instrument emits ground waves that travel laterally in a shallow
zone of the soil. Depending on their frequency, the waves can penetrate
up to one-half meter. The researchers take measurements using multiple
frequencies and, combined with other projected data generated by
a mathematical model, generate an accurate profile of the moisture
around the roots of the vines.

"Once we identify the topology of the field, we can provide
just six or so pivot points in a block (approx. 300 meters squared)
that the farmers can check biweekly," Rubin says. "Collecting
information from those points provides enough data to determine
an irrigation schedule."

In what
ways do you believe high-technology geophysics will impact
the California wine business?

Firm control over stressed irrigation, Rubin says, also enables
grape farmers to create uniform ripening patterns. Rather than
return to the same plot multiple times during a harvest, farmers
could increase efficiency by collecting all the fruit at one time,
he explains. These techniques may provide insight into the biology
of the vines as well.

"We'd like to understand which parts of the plant get water
from particular soil depths." Rubin says. "For example,
do the vines need uniform moisture to thrive?"

To answer these questions, Rubin is currently working on a proposal
to collaborate with Todd Dawson, a UC Berkeley professor of Integrative
Biology, on the next phase of the vineyard project. The hope is
that, by combining the soil moisture profiles with Dawson's
isotope analysis, a method used to determine distribution of certain
elements in a material, the researchers will be able to produce
a high-resolution picture of how the vines drink from the soil.

Lab Notes is
published online by the Public Affairs Office of the UC Berkeley
College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will
dramatically change our lives tomorrow.